Statistics

Components of Reproductive Isolation between Subspecies of an Annual Plant

Reproductive isolation is required in the divergence of species. The components of reproductive isolation are separated into either ecological or genetic components. In plants these include: habitat, temporal, pollinator fidelity, gametic incompatibility, zygotic mortality, hybrid viability, male and female hybrid sterility and hybrid breakdown. Cleistogamy, the production of closed obligate self-fertilizing flowers, creates a barrier to gene flow by preventing hybridization. However, there have been few studies that have investigated its impact in reproductive isolation. A unique opportunity arose to determine the degree of isolation that cleistogamy provides. In multiple sites within Pitt County two subspecies of an annual, cleistogamous plant Triodanis co-occur. Each subspecies exhibit a mixture of cleistogamous and open (Chasmogamous) flowers. Soil moisture and content were quantified at several sites where they co-occur to calculate the extent that each contributes to the isolation of the two subspecies. Calculations show that there are significant differences in the soil for moisture, content and ability to hold water. Observations in the field were also made to calculate the overlap of flowering and it was found that the species do in fact overlap, therefore, unlikely to impact prezygotic isolation. To quantify the extent of postzygotic isolation due to cleistogamy, the number of seeds produced was quantified between open and closed flowers. By using hand pollination, an F1 generation was made and raised in the greenhouse to calculate viability (survivorship and biomass). Results show that F1's are in fact viable and in some cases appear to be as large or larger than parentals. A variety of other reproductive barriers were also quantified, allowing us to determine the total amount of isolation for each subspecies as well as the relative amount of isolation due to cleistogamy. This study is essential to the understanding of cleistogamy as a component of reproductive isolation both pre and postzygotic.